Rotary cutter drums

ABSTRACT

The invention provides a rotary cutter drum for use in apparatus for cutting continuous web material into discrete lengths in which the polar moment of inertia is kept to a minimum. The drum consists of a prefabricated metal load bearing member to which a block, on which a knife blade is mounted, and a balancing member are secured. The load bearing member, the block and the balancing member are then covered in a lightweight material such as an integral skin polyurethane rigid foam material arranged so that the outer surface of the whole drum is rotational symmetrical, the surface being interrupted to allow for the mounting of the knife blade.

This invention concerns improvements in or relating to rotary cutterdrums and in particular to cutter drums for use in apparatus for cuttingcontinuous webs of material into discrete lengths.

As said cutter drums, e.g. in paper cutters, are required to operate athigh speeds it has been found desirable to form their cutter surfaces soas to create minimum air turbulence, to avoid disturbance of the webadjacent to the cutting region. Also, it is advantageous to keep thepolar moment of inertia of such drums to a minimum.

It is an object of the present invention to provide a form of cutterdrum which while relatively simple satisfies both the aboverequirements.

According to the present invention there is provided a rotary cutterdrum for use in apparatus for cutting continuous web material intodiscrete lengths including a load carrying member, means for attachmentof a cutter blade thereto, and non-load carrying light-weight materialsecured to said load carrying member and so arranged that the wholeforms a body whose outer surface is a surface of revolution, orotherwise rotationally symmetrical, interrupted as ncessary to allow forthe presence of such cutter blade.

Generally machines for cutting continuous web material into lengthsoperate at high speeds, so it is preferable that means is provided onsaid load carrying member to balance said cutter blade and saidattachment means.

The cutter drum may further include a pair of end members between whichsaid load carrying member and said attachment means extend, each of saidend members being secured to one end of said load carrying member andsaid attachment means. Conveniently said attachment means may comprise amounting block having a longitudinal recess formed therein and in whichsaid cutter blade is mounted, said mounting block being secured to saidload carrying member.

In a preferred form the load carrying member consists of a number ofelements secured together, for example, by welding, and the use of alight-weight material for forming said body keeps to a minimum the polarmoment of inertia of the cutter drum. Conveniently said light-weightmaterial may be a rigid plastics foam, such as a structural polyurethanefoam.

Where it is necessary to provide a drum in which the cutter blade hasits cutting edge at such a radius from the rotational axis of said drumthat it is not possible to attach said cutter blade directly to saidload carrying member, means may be provided projecting from said loadcarrying member and to which said cutter blade is attached. In thisconstruction the balancing means must also balance said projecting meansand the light-weight material is secured to said load carrying memberand said projecting means.

A cutter drum constructed according to the present invention enables thedrum to be made with a smaller diameter than conventional drums, whilstretaining required stiffness of the drum. Consequently the polar momentof inertia of a drum according to the invention is less than that of aconventional drum.

A preferred embodiment of the invention will now be described by way ofexample with reference to the accompanying drawing which shows a rotarydrum broken in two to show its internal details.

plate;

Referring to the drawing, a rotary drum 1 for use in a machine forcutting a continuous web of paper into discrete lengths has two endsmembers 2 each consisting of a disc 3 of steel plate from which extendsa central stub shaft 4. Through one of the shafts 4 a rotary drive maybe imparted to the drum 1, from a drive mechanism (not shown). A loadcarrying member 5 extends between and is fixed at opposite ends thereof,to the two discs 3. The member 5 consists of three elements, namely atransverse web 6 of steel plate having a width equal to the diameter ofthe discs 3, and a pair of secondary webs 7 of steel plate, secured tothe webs 7 of the member 5 is a mounting block 8, and a bar 9 of steelis secured to the web 6 of member 5 diametrically opposite the mountingblock 8, the bar 9 being used for balancing the mass of the drum 1 andincreasing its stiffness. The various parts 6, 7, 8 and 9 are weldedtogether and are also welded, at opposite ends, to the discs 3. Alongitudinal recess 10 is then formed in the block 8 and discs 3, andthe outer surfaces of the mounting block 8 and bar 9, and also thenarrow longitudinal edges of the web 6, are machined to conform to theouter peripheral surface of the drum 1. A knive blade 11 is mounted inthe recess 10 in any convenient known manner, the mounting block 8 anddiscs 3 being cut away, as shown at 14, to provide space for means (notshown) for holding the knife blade 11 in the recess 10. An example of apreferred mounting for the knife 11 is described and illustrated in U.S.Pat. application Ser. No. 481,865 filed 21st June 1974, now U.S. Pat.No. 3,935,774.

With the end members 2, load carrying member 5, block 8 and bar 9constructed as described above, a rotary drum of low polar moment ofinertia is provided, the member 5, block 8 and bar 9 providing adequatestiffness to the drum over its length. However, such a drum, because ofits paddle wheel like shape in cross section, would cause considerableair turbulence when in use which would have a disturbing effect on theweb of paper to be cut. In order to reduce this turbulence, withoutsubstantially increasing the polar moment of inertia of the drum, it hasbeen found convenient to fill the spaces bounded by the web 6, andsecondary webs 7 and block 8, and also the web 6 and the bar 9, betweenthe discs 3, with a light-weight material 12, which may consist of, forexample, a rigid plastics foam, such as a structural polyurethane foam,having an outer skin of adequate hardness and strength to withstand allnormal usage. An example of a satisfactory material is integral skinpolyurethane rigid foam type "Bibbicast RM400" produced by BibbyChemicals Limited, of Accrington, England.

In order to fill the spaces mentioned above with foam, the entire weldedassembly is placed in a closely fitting cylindrical mould andpolyurethane plastics foam mix is introduced in any known manner, suchas injection or gravity feed. If required, the welded assembly could bereplaced by a suitable metal casting, but however the load carryingmember is constructed, the inside surface of the cylindrical mould iscoated with a suitable release agent prior to the foam material beingpoured into the mould. To ensure that the polyurethane foam bonds to theload carrying member 5 and discs 3, it is usually only necessary toprovide a clean and grease free surface. However, should this provedifficult to achieve then mechanical bonding can be adopted such asroughening those surfaces of the parts 3, 6, 7, 8 and 9 contacted by thefoam material. Alternatively objects around which the foam can key maybe fixed to the surfaces of the load carrying member 5, block 8 and bar9, or holes 13 can be provided in the transverse web 6 to join the twoadjacent cavities. If damage occurs to the outer surface of the foam, orpart of the foam has to be removed for some reason, then a repair caneasily be achieved by placing a part mould over the affected area andintroducing fresh foam material.

I claim:
 1. A rotary cutter drum for use in apparatus for cuttingcontinuous web material into discrete lengths including a load carryingmember, means for attachment of a cutter blade thereto, and non-loadcarrying light-weight material secured to said load carrying member andso arranged that the whole forms a body whose outer surface isrotationally symmetrical, interrupted as necessary to allow for thepresence of such cutter blade, in which means is provided on said loadcarrying member to balance said cutter blade and said attachment means.2. A rotary cutter drum as claimed in claim 1 further including a pairof end members between which said load carrying member and saidattachment means extend, each of said end members being secured to oneend of said load carrying member and said attachment means.
 3. A rotarycutter drum as claimed in claim 2 in which said load carrying memberconsists of a number of elements secured together.
 4. A rotary cutterdrum as claimed in claim 3 in which said attachment means comprises amounting block having a longitudinal recess formed therein and in whichsaid cutter blade is mounted, said mounting block being secured to saidload carrying member.
 5. A rotary cutter drum as claimed in claim 4 inwhich said light-weight material is a rigid plastics foam material.
 6. Arotary cutter drum as claimed in claim 5 in which said rigid plasticsfoam material is a structural polyurethane foam.